Methods for improving uplink (UL) coverage, throughput, and transmission latency are currently being investigated in Release 6 of the Third Generation Partnership Project (3GPP). In order to achieve these goals, the Node-B will take over responsibility of scheduling and assigning UL resources to WTRUs. The Node-B can make more efficient decisions and manage UL radio resources on a short-term basis better than an RNC. The RNC still retains coarse overall control of the cell with enhanced uplink (EU) services so that the RNC can perform functions such as call admission control and congestion control.
Hybrid-automatic repeat request (H-ARQ) techniques provide a procedure for generating transmissions and retransmissions with low latency. A primary aspect of H-ARQ techniques is that data received in failed transmissions is soft combined with successive retransmissions to increase the probability of successful reception.
When an H-ARQ scheme and Node-B scheduling of transmissions is used, the time required to successfully transmit data will vary. Applications requiring very low latency transmission can be adversely effected by significantly delayed transmissions. For example, delayed data may be considered to be a failed transmission and end up being unnecessarily retransmitted by the application. Therefore, a mechanism that limits transmission latency is required.